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DeflateStream Class

Updated: August 2009

Provides methods and properties for compressing and decompressing streams using the Deflate algorithm.

Namespace:  System.IO.Compression
Assembly:  System (in System.dll)
public class DeflateStream : Stream

This class represents the Deflate algorithm, an industry standard algorithm for lossless file compression and decompression. It uses a combination of the LZ77 algorithm and Huffman coding. Data can be produced or consumed, even for an arbitrarily long, sequentially presented input data stream, using only previously bound amount of intermediate storage. The format can be implemented readily in a manner not covered by patents. For more information, see RFC 1951. "DEFLATE Compressed Data Format Specification version 1.3." This class cannot be used to compress files larger than 4 GB.

This class does not inherently provide functionality for adding files to or extracting files from .zip archives.

The GZipStream class uses the gzip data format, which includes a cyclic redundancy check value for detecting data corruption. The gzip data format uses the same compression algorithm as the DeflateStream class.

The compression functionality in DeflateStream and GZipStream is exposed as a stream. Data is read in on a byte-by-byte basis, so it is not possible to perform multiple passes to determine the best method for compressing entire files or large blocks of data. The DeflateStream and GZipStream classes are best used on uncompressed sources of data. If the source data is already compressed, using these classes may actually increase the size of the stream.

The following example shows how to use the GZipStream class to compress and decompress a directory of files.

using System;
using System.IO;
using System.IO.Compression;

public class Program
{

    public static void Main()
    {
        // Path to directory of files to compress and decompress.
        string dirpath = @"c:\users\public\reports";

        DirectoryInfo di = new DirectoryInfo(dirpath);

        // Compress the directory's files. 
        foreach (FileInfo fi in di.GetFiles())
        {
            Compress(fi);
    	}

        // Decompress all *.cmp files in the directory. 
        foreach (FileInfo fi in di.GetFiles("*.cmp"))
        {
    		Decompress(fi);
        }


    }

    public static void Compress(FileInfo fi)
    {
        // Get the stream of the source file. 
        using (FileStream inFile = fi.OpenRead())
        {
            // Prevent compressing hidden and already compressed files. 
            if ((File.GetAttributes(fi.FullName) & FileAttributes.Hidden)
                != FileAttributes.Hidden & fi.Extension != ".cmp")
            {
                // Create the compressed file. 
                using (FileStream outFile = 
                        File.Create(fi.FullName + ".cmp"))
                {
                    using (DeflateStream Compress = 
                        new DeflateStream(outFile, 
                        CompressionMode.Compress))
                    {
                        // Copy the source file into  
                        // the compression stream.
                        byte[] buffer = new byte[4096];
                        int numRead;
                        while ((numRead = inFile.Read(buffer, 
                                0, buffer.Length)) != 0)
                        {
                            Compress.Write(buffer, 0, numRead);
                        }
                        Console.WriteLine("Compressed {0} from {1} to {2} bytes.",
                        fi.Name, fi.Length.ToString(), outFile.Length.ToString());
                    }
                }
            }
        }
    }

    public static void Decompress(FileInfo fi)
    {
        // Get the stream of the source file. 
        using (FileStream inFile = fi.OpenRead())
        {
        	// Get original file extension,  
            // for example "doc" from report.doc.cmp.
        	string curFile = fi.FullName;
        	string origName = curFile.Remove(curFile.Length 
                    - fi.Extension.Length);

        	//Create the decompressed file. 
        	using (FileStream outFile = File.Create(origName))
        	{
        	    using (DeflateStream Decompress = new DeflateStream(inFile,
        		    CompressionMode.Decompress))
        	    {
            		//Copy the decompression stream into the output file.
            		byte[] buffer = new byte[4096];
            		int numRead;
            		while ((numRead = 
                        Decompress.Read(buffer, 0, buffer.Length)) != 0)
            		{
            		    outFile.Write(buffer, 0, numRead);
            		}
            		Console.WriteLine("Decompressed: {0}", fi.Name);
        	    }
        	}
        }
    }
}
System.Object
  System.MarshalByRefObject
    System.IO.Stream
      System.IO.Compression.DeflateStream
Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0

.NET Compact Framework

Supported in: 3.5

XNA Framework

Supported in: 3.0

Date

History

Reason

August 2009

Improved code example.

Information enhancement.

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